The invention relates to methods and apparatus for subsurface testing. More specifically the invention relates to methods and apparatus for evaluation of subsurface moisture content.
Water and associated contaminants seep into the ground and travel through a subsurface region known as the vadose zone (a region of unsaturated soil). How the water and associated contaminants move in the vadose zone, to a large degree, determines how much contamination (such as gasoline additives, agricultural chemicals, or buried nuclear waste leakage) may end up in a water supply (such as an aquifier). Therefore, gaining an understanding of how the water and associated contaminants move in the vadose zone is valuable for appropriate waste containment. Information regarding the movement of water and associated contaminants in the vadose zone is generally acquired through the use of subsurface probes or similar testing devices. Several apparatus and methods have been used to facilitate such testing and information gathering. Some of these apparatus and methods involve obtaining samples of subsurface liquids, while others test soil moisture or other parameters.
One particular type of device which has proven useful in gathering information is a tensiometer. The tensiometer is a hydrological instrument which is used to determine the moisture content of unsaturated soils or other substrates. The tensiometer measures xe2x80x9cmatric potentialxe2x80x9dxe2x80x94a measure of how tightly water is held under tension in an unsaturated environment. By grouping several tensiometers at different depths, water gradients can be determined. This in turn allows one to determine the direction and rate of water flow within the unsaturated substrate.
Although prior tensiometers have been useful in gathering information, such tensiometers have shortcomings which have limited their usefulness. For example, prior tensiometers typically cannot be installed in highly contaminated areas without prior excavation or drilling, and in contaminated areas such excavation or drilling is highly undesirable as it would tend to spread contamination.
Monitoring and testing to determine the movement of subsurface water and associated contaminants is particularly valuable when dealing with waste disposal sites that contain radiological contaminants or other hazards. However, as described above, placing probes into the subsurface for data collection in such sites has not been feasible, because the placing of such probes would require drilling or coring which would bring contaminated xe2x80x9ccuttingsxe2x80x9d to the surface and would create a pathway through which contaminated emissions may escape. As a result, testing probes have typically been placed in areas around such waste sites. Unfortunately, such probe placement only provides information when the contaminants have already migrated outside of the waste disposal site area. Moreover, at the point when the contaminants have already migrated outside of the waste disposal site area, it is likely that a major contaminant plume already exists in the subsurface soil and aquifer making remediation and containment efforts much more difficult and costly.
In view of the foregoing, it would be highly desirable to provide methods and apparatus which facilitate subsurface testing in both contaminated and non-contaminated areas, while substantially avoiding these and other shortcomings of the prior devices.